Thin Men carry plasma rifles, so always try and capture those creepy alien dudes alive. You'll also get free intact weapons for your troops. Using an arc thrower to stun an enemy is not just for research. You can always use nicknames (like "Doc" or "Grenades") to remind you who's who. If you have a support class who can hold three medikits, for Christ's sake give her a medikit. Make sure you mix the right equipment with the right skills. Shotguns are extremely powerful, but force you to put your soldiers in very up-close-and-personal encounters with the aliens. Remember: you can always instruct them to switch back to an assault rifle before the battle begins. Newly appointed assault units will automatically switch to a shotgun. If you're in danger and need a lot of damage with a lot of accuracy, go loud.
Pesky Dr Vahlen will remind you that blowing up an alien makes it impossible to examine it for research, but a few Sectoid corpses and a weapon fragment is just not worth the risk. Feel free to move a soldier forward, and then boss someone else about for a bit to better assess the situation. Each unit gets to make two moves on the battlefield, but you don't have to issue both orders at once. Move deliberately between close cover points, and make gratuitous use of overwatch to cover your arse against ambushes. Dashing to a faraway cover point is a surefire way to get your unit killed. The sniper's battle scanner perk is also very useful for seeing through the fog of war.
Get them up high (either by climbing ladders or using the Archangel armour / grappling hook), and keep them on overwatch. Snipers are the most essential units, and will often be the deciding factor in a tough battle.
XCOM ENEMY WITHIN STARTING COUNTRY UPGRADE
The ammo conservation upgrade in the foundry is also highly recommended.
XCOM ENEMY WITHIN STARTING COUNTRY FULL
You don't want to be running on empty when you stumble into a room full of Mutons. Always reload your weapons during the downtimes between battles. These tips and tricks will be absolutely perfect for newcomers to the series. To help you answer these questions, and more, here's a quick-fire guide to get you started in Enemy Unknown. On what should I focus my monthly funding? How do I stop China from pulling out of the XCOM project? What's the best unit to take? Where should I focus my research? Whether you're hunkered down on the battlefield or trying to balance your budget back at headquarters, there are always so many decisions to make and so many options from which to choose.